Storage tanks used in fueling environments are usually located underground. Liquid fuels such as gasoline or diesel are stored in bulk until they are dispensed to customers by means of the station's fueling equipment. Environmental compliances require that monitoring systems be in place to determine inventory and leakage. Many types of equipment are used to perform this measurement. In this invention, we are going to focus on the use of a Magnetostrictive probe, which is the most commonly used detection apparatus employed in this industry.
Similar to its use in this application, the Magnetostrictive probe is fitted into a tank, and is comprised of a shaft that protrudes over the height of the entire tank. Detections and logic circuitries are located inside of a canister usually situated on top of the shaft. The probe and other accessories, like floats are introduced into the tank via a riser pipe connected to the tank. The means of ascertaining the levels, “fuel” and “water”, are commonly through the utilization of floating bodies each carrying a magnet. The floats are often constructed of materials such as Nitrophyl, Buna-N, Urethane and Stainless Steel. In the tank, floats are calibrated to have densities that are less than the fuel they are intended to monitor in order to float at the surface of said liquid; in this case gasoline products. Floats are allowed to sink into a fuel layer to stop at the interface of another fluid where the buoyant forces exerted by the combined fuels matches the density of the float in question. In this instance, the float remains at the interface of the two fuels. By this method, the systems are not limited to only two floats. A multiplicity of such floats could be adapted into a single probe intended to be used in a tank having various fluids of different densities.
The Magnetostrictive probe detection apparatus is set to locate the presence of a magnet along the shaft by means of an interaction between the permanent magnetic field emanating from the magnet and the circumferential field introduced into the Nichrome wire within the shaft by the application of a current pulse into that said wire. With the float slidably disposed along the probe's shaft and carrying the magnet that is intended to report its location, the system is able to locate the exact position of the float along the shaft. This is accomplished by means of the known propagation velocity of the twist resulting from the interaction between the two magnetic fields mentioned earlier. The delta time from when the current pulse was applied to the time a resulting twist is detected represents the time interval taken for the wave to propagate along the wire medium from its origin. When that time “T” is divided by the known propagation velocity in that wire, the magnet's exact location is then calculated by the system.
The intent of this invention is purely for fuel quality determination. With water capable of entering the tank by many means, such as a leaky tank, condensation, a poorly sealed tank, vent pipe etc. the possibility for water accumulation at the tank's bottom had always been a problem faced by this industry. However, previous to the time when ethanol was introduced as a means of controlling pollution, the water used to remain at the bottom of the tank where it would be accumulated and gets detected by the float that was designed to work in the interface of gasoline and water. Ethanol's affinity to absorb water creates a different problem that renders inoperative the current floats used in the industry. This invention' sole intent is to help overcome this problem.
When water enters a tank containing 10% ethanol by volume, or E10, the water is absorbed by the alcohol content of the fuel and remains suspended in the gasoline until the water and ethanol ratio exceeds a threshold. When this state is reached, the combined solution precipitates out of the fuel and resides at the bottom of the tank. This solution has a density lower than that of water and the interface behaves very closely to that of gasoline, which confuses present water detection systems.
This newly formed aqueous solution is different than water in density, thus making it difficult for a float that was designed to work at the boundary of gasoline and water to have the right buoyant force necessary to lift it from the tank's bottom. In some instances, when the ratio of water in the solution is high enough, the float is lifted but it takes a considerable level of this solution to achieve this. In that case, the true height of this solution is not properly reported by the probe and jeopardizes the quality of the fuel dispensed and the integrity of the gas station's brand.